This invention relates to enzymatic sensor electrodes and their combination with reference electrodes to detect a compound in a liquid mixture.
Various electrochemical sensors are known which employ enzymes to sense the presence of a compound that serves as an enzyme substrate. As just one example, Nakamura U.S. Pat. No. 4,224,125 discloses an enzyme electrode system in which an enzyme, such as glucose oxidase, is used to sense glucose. A redox compound is used to accept electrons from the enzyme. For example, at 10:21-49, Nakamura discloses (FIG. 5) press molding to the electrode a mixture of glucose oxidase cross-linked by gluteraldehyde and a fluorocarbon polymer powder together with a cation exchange resin containing potassium ferricyanide. Nakamura's electrode system (FIG. 2) consists of three electrodes: an enzyme electrode 7, a reference electrode 8, and a counter electrode 10.
In another example, Pace U.S. Pat. No. 4,225,410 discloses a multi-layer enzyme sensor; for example sensor 14b (FIG. 7b) measures levels of lactate dehydrogenase. NAD.sup.+ is generated at a fourth electrode 82, and the enzymatic reaction converts it to NADH which is sensed at monitoring electrode 84 by undisclosed means. A barrier/counter electrode 80 and a reference electrode 85 are used in conjunction with monitoring electrode 84.